Numerical study on hydrodynamic effect of flexibility in a self-propelled plunging foil
Numerical study on hydrodynamic effect of flexibility in a self-propelled plunging foil
复制标题
自航潜水翼柔性水动力效应数值研究
DOI：
10.1016/j.compfluid.2014.03.031
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发表时间：
2014-06
期刊：
影响因子：
--
通讯作者：
Zhang X
中科院分区：
文献类型：
--
作者：
Zhu XJ;He GW;Zhang X
本研究是一个数值研究的水动力效应的被动柔性的自航暴跌箔。在模型问题中，流动是二维的，不可压缩的和层流的，而柔性箔被视为不可伸展的细丝。翼片的前缘在垂直方向上经历规定的谐波振荡。在水平方向上，箔片自由移动并且不施加约束。模拟是通过使用一个求解器耦合的沉浸边界法的流动和有限差分法的结构。系统的参数研究已经进行了调查的重要物理量，如巡航速度，游泳功率和推进效率的灵活性的影响。结果发现，最佳巡航速度总是在一些被动的灵活性，而不是刚性的箔。另一个重要的发现是，最佳性能总是在比谐振点低得多的强迫频率下实现。基于仿真结果，随着弯曲刚度的增加，自航翼片的三种动力学状态被识别出来，非周期性运动、周期性后退运动和周期性前进运动。对于向前运动的柔性翼，取决于弯曲刚度的范围，偏转或对称的涡街作为特征尾流结构出现。研究发现，适度的柔度有利于尾流对称性的保持，而过大的柔度则会引发尾流对称性的破缺。在当前的工作中获得的结果揭示了一些灵活性的作用，在拍打为基础的biolocomotion。
The present study is a numerical investigation of the hydrodynamic effects of passive flexibility on a self-propelled plunging foil. In the model problem, the flow is two-dimensional, incompressible and laminar, while the flexible foil is treated as an inextensible filament. The leading-edge of the foil undergoes a prescribed harmonic oscillation in the vertical direction. In the horizontal direction, the foil is free to move and no constraint is imposed. The simulations are performed by using a solver which couples the immersed boundary method for the flow and the finite difference method for the structure. A systematic parametric study has been conducted to investigate the effects of flexibility on important physical quantities such as the cruising speed, swimming power and propulsive efficiency. It is found that optimal cruising speed is always achieved in foils with some passive flexibility and not the rigid ones. Another important finding is that optimum performance is always achieved at a forcing frequency much lower than the resonance point. Based on the simulation results, three dynamical states of a self-propelled foil have been identified with the increase of bending rigidity, i.e., non-periodic movement, periodic backward-movement and periodic forward-movement. For a flexible foil in forward movement, depending on the range of bending rigidity, either a deflected or a symmetric vortex street arises as the characteristic wake structure. It is found that moderate flexibility is beneficial to symmetry preservation in the wake, while excessive flexibility can trigger symmetry-breaking. The results obtained in the current work shed some light on the role of flexibility in flapping-based biolocomotion.
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影响因子：
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